A lithium ion secondary battery will be first described.
FIG. 2 schematically illustrates an operation principle of a lithium ion secondary battery, and a reference numeral 100 denotes a lithium ion secondary battery, a reference numeral 100a denotes a battery can, a reference numeral 101 denotes a positive electrode, a reference numeral 101a denotes a positive electrode active material, a reference numeral 102 denotes a negative electrode, a reference numeral 102a denotes a negative electrode active material, a reference numeral 103 denotes a separator, and a reference numeral 104 denotes an electrolyte.
In FIG. 2, the lithium ion secondary battery 100 has a configuration in which the positive electrode 101 having an active material 101a of a metal oxide such as lithium, the negative electrode 102 having an active material 102a of a carbon material, the electrolyte 104 having an organic solvent and a lithium salt, and the separator 103 are placed within the electrode can 100a. The positive electrode 101 and the negative electrode are film-formed, and form a cylindrical electrode pair corresponding to a cylindrical shape of the electrode can 100a with a film-like separator 103 interposed therebetween. Such an electrode pair is placed in the electrolyte 104 which is injected into the electrode can 100a. One electrode pair having the positive electrode 101 and the negative electrode 102 is here illustrated within the electrode can 100a; however, a plurality of the electrode pairs are provided and these are connected to in series each other.
In the lithium ion secondary battery 100 having such a configuration, when a lithium ion moves between the positive electrode 101 and the negative electrode 102, charging and discharging is performed. When the charging is performed under a usage environment, a lithium ion of the positive electrode 101 moves to the negative electrode 102 and the charging is performed. When the discharging is performed under a usage environment, a lithium ion of the negative electrode 102 moves to the positive electrode 101. As described above, the lithium ion secondary battery 100 has an operation principle without a chemical reaction in terms of the principle, and therefore has a feature in which a life is long and energy efficiency is high.
Hereinafter, one lithium ion secondary battery having a configuration illustrated in FIG. 2 is referred to as a “single battery”, and one lithium ion secondary battery having a configuration in which a plurality of the single batteries are incorporated thereinto is referred to as a “module battery”.
FIG. 3 schematically illustrates a manufacturing process of the single battery and module battery of the lithium ion secondary battery.
In FIG. 3, the manufacturing process of the lithium ion secondary battery 100 includes a positive electrode material manufacturing process 110, a negative electrode material manufacturing process 111, an assembling process of the single battery 112, and an assembling process of the module battery 113.
In the positive electrode material manufacturing process 110, various materials as a raw material of the positive electrode material are kneaded, blended, and slurry materials are prepared. After the slurry materials are coated on a film-like metallic foil, processing such as compression and cutting is performed to the metallic foil on which the slurry materials are coated, and the film-like positive electrode materials are manufactured.
Various materials as a raw material used in the negative electrode material manufacturing process 111 are different from those in the positive electrode material manufacturing process 110, however, procedures are the same as each other. Various materials as a raw material of the negative electrode material are kneaded, blended, and slurry materials are prepared (kneading and blending). After the slurry materials are coated on a film-like metallic foil (coating), processing such as compression and cutting is performed to the metallic foil on which the slurry materials are coated (processing), and the film-like negative electrode materials are manufactured.
In the assembling process 112 of the single battery of the lithium ion secondary battery, a positive electrode and a negative electrode having a size necessary for the single battery are cut out from the film-like positive electrode materials and negative electrode materials in a process referred to as winding. At the same time, a separator having a size necessary for the single battery is cut out from the film-like separator materials for separating these positive electrode materials and negative electrode materials, and these positive electrode and negative electrode are wound in piles with the separator interposed therebetween (winding). A group of the electrode pair of the wound positive electrode, negative electrode, and separator is assembled and welded. After a group of the electrode pair is arranged in the electrode can into which an electrolyte is poured (pouring), this battery can is completely sealed (sealing). In this way, the single battery is manufactured.
Next, the charging and discharging is repeated in the single battery of this manufactured lithium ion secondary battery, and an inspection relating to the performance and reliability of the single battery of this lithium ion secondary battery is performed (single battery inspection). Through the process, the single battery is completed and the single battery assembling process is terminated.
Next, in the module battery assembling process 113, a plurality of the single batteries are assembled in series, and further the controller is connected thereto to manufacture the module battery (module assembling). Thereafter, an inspection relating to the performance and reliability of the module battery of the lithium ion secondary battery is performed (module inspection). Through the process, the module battery of the lithium ion secondary battery is completed and shipped.
FIG. 4 is a flowchart illustrating a procedure of a method for charging the lithium ion secondary battery. This charging method is performed at the time of the “charging and discharging” and “single battery inspection” in the single battery assembling process 112 of FIG. 3, and at the time of the “module inspection” in the module battery assembling process 113.
In FIG. 4, when the lithium ion secondary battery is loaded in the charging device, a check of the connection is performed (step S100) and a check of the temperature is performed (step S101). If abnormality is not present in the checks, a voltage of the lithium ion secondary battery before the charging is measured (step S102). If the connection state, temperature, and voltage of the lithium ion secondary battery before the charging are deviated from a predetermined range (“No” at steps S100, S101, and S103), it is determined that the lithium ion secondary battery is abnormal and the charging processing is terminated (step S107).
If the connection state, temperature, and voltage of the lithium ion secondary battery before the charging fall within the predetermined range and are normal (“Yes” at steps S100, S101, and S103), a constant voltage is applied to the lithium ion secondary battery to perform the charging (step S104). During the charging processing, while the time necessary for the charging is checked, a current of the lithium ion secondary battery is measured, and until a current value becomes smaller than a predetermined value, the charging processing is repeated (repetition of step S105, “No” at step S106, and step S104). Before the charging time reaches a predetermined value (“Yes” at step S105), when the current value becomes smaller than the predetermined value (“Yes” at step S106), it is determined that the lithium ion secondary battery is normally charged, and the charging is terminated. However, even if the charging time reaches the predetermined value, when the current value fails to become smaller than the predetermined value (“No” at step S105), it is determined that the abnormality is present and the charging processing is terminated (step S107).
In this way, the module battery of the lithium ion secondary battery in which a normal charging result is obtained is shipped in a charged state and used under a usage environment by a user who purchases it.
FIGS. 5A and 5B schematically illustrate a transition of the voltage and current during the charging processing of the lithium ion secondary battery.
The voltage of the lithium ion secondary battery during the charging increases following the charging processing. On the other hand, while keeping a constant state, the charging current is rapidly reduced at a stage in which the charging is nearer to the completion.
When the charging of the lithium ion secondary battery is performed, a voltage normally remains in the secondary battery. FIG. 5A illustrates a transition of the voltage and current during the charging processing at the time when a start voltage of the charging is set to the residual voltage of the lithium ion secondary battery. In this case, when the lithium ion secondary battery is loaded in the charging device, the charging processing is immediately performed.
As compared with the above, in FIG. 5B, when the lithium ion secondary battery is loaded in the charging device, an electricity which remains in the lithium ion secondary battery is first discharged and the residual voltage is set to zero volt. Thereafter, this zero volt is set as the charging start voltage, and the charging processing is started. In this case, the charging current first flows from the lithium ion secondary battery, and thereafter the voltage increases following the charging processing as described above. On the other hand, while keeping a constant state, the charging current is rapidly reduced at the stage in which the charging is nearer to the completion.
The lithium ion secondary battery is used by repeating the charging and discharging. For the purpose of securing safety and reliability of the lithium ion secondary battery, the voltage and current of the lithium ion secondary battery during the charging or discharging are measured. A diagnosis for grasping whether a problem arises in the performance of the lithium ion secondary battery is performed based on the measurement result.
As one conventional example, there is proposed a technique in which an internal impedance is calculated based on a voltage and current of the battery and a life of the battery is diagnosed (see, for example, JP-A-2006-524332).
As another conventional example, there is also proposed a technique in which voltage and current characteristics during charging and discharging are measured, a characteristic factor is digitized from a measurement result of characteristic impedance to a predetermined frequency zone, and a state of a battery is diagnosed, and further a battery used in a module according to the battery characteristic is selected also in a manufacturing process in order to secure safety and reliability (see, for example, JP-A-2000-156248).
As another conventional example, there is further proposed a technique of classifying a single battery having a similar spectrum based on an impedance spectrum of the battery by using a pattern matching technique and improving reliability of a module battery by selecting the single battery so as to reduce a standard variation in the module battery (see, for example, JP-A-10-312823).